1. Field of the Invention
The present invention relates to a process for depositing desired films on the surface of a substrate, and to an apparatus for film deposition.
2. Prior Art
Referring to a schematically drawn view in FIG. 7, a conventional process for depositing a film on a substrate is described below.
A film deposition chamber 71 comprises a substrate support 73 for mounting thereon a substrate 72 to deposit a film on the surface thereof, a cathode 74 for applying high frequency power to activate the product gas to deposit a film on the surface of the substrate 72, an inlet 75 for introducing product gas as a starting material for the film, and an outlet 76 for controlling the pressure inside the chamber to facilitate film deposition on the substrate 72.
The cathode 74 is connected to a high frequency power source 78 to apply a power to the product gas for the activation of the gas. The substrate support 73 is heated by a heater 79 to control the temperature thereof to provide a condition suited for film deposition.
In depositing an amorphous silicon film by plasma-assisted chemical vapor deposition (plasma CVD) using monosilane as the starting material, for instance, a high frequency power of 13.56 MHz is applied to the cathode 74 while controlling the pressure inside the film deposition chamber 71 to 300 mTorr and the temperature of the substrate 72 to 300.degree. C. A plasma forms on introducing monosilane as the product gas into such a film deposition chamber 71 having its temperature and pressure suitably controlled to obtain an amorphous silicon film deposit on the substrate 72 being heated with a heater 79. The film can be deposited on the surface of the substrate 72 not only by plasma CVD, but also by a process such as photochemical vapordeposition (photo-CVD), thermal CVD, physical vapor deposition (PVD), deposition using electron cyclotron resonance, vapor deposition, sputtering, and laser ablation.
Various types of films can be deposited on the substrate 72 in the place of the amorphous silicon film above, and included are a diamond film, a ceramics film, a semiconductor film, an insulator film, a metallic film, and a superconductor film.
An amorphous silicon film having deposited by plasma CVD process at a low temperature (any temperature from room temperature to 100.degree. C.), however, suffers poor photo-conductivity. An improved photoconductivity can be obtained only by elevating the temperature of the substrate to, for example, 300.degree. C.
When a substrate such as a polymer film having inferior resistance against heat is used, however, the process above cannot be applied. Furthermore, when the substrate is heated to 300.degree. C. in fabricating solar cells, transistors of liquid crystal panels, etc., the substrate readily undergoes reaction with the transparent electrode during the film deposition.
In addition to the shortcomings above, it further is a problem in vapor phase synthesis because it comprises vapor phase reaction and surface reaction in which the latter cannot be controlled.
The present invention is accomplished for overcoming the problems above, and it provides a film deposition process for depositing films on the surface of a substrate at a low temperature while rendering desired characteristics to the deposited film. The present invention also provides an apparatus for depositing such films.